Battery safety li-po

[Casper]

http://www.volarenparamotor.com/blog/2017/11/ojo-con-las-baterias-de-li-po-en-el-paramotor/

Sadly it was just a matter of time before something like this would happen. If you use li-po and have a safety bag around the battery, make sure that it actually works! some of them just claim to work but in reality they are useless and won't contain the flames when they expand from the built up pressure. Also use batteries together with a protection circuit.

[AndyB]

As I have said before, I have flown elec radio controlled planes for nearly 20 years. Many of my planes push the batteries to their limits of current, temperature and duration. However, I have NOT had a single fire in flight.  I have had rectangular batteries turn into near spherical balls after expanding. I have had cell failures, loading up other batteries. still no fires in flight. 

The above story is more like a "scare story". it has no details. It may as well be a story showing someone lighting a campfire on his lap ad then saying "campfires are dangerous when flying|"

My own experience shows that just following simple rules means the LiPos remain safe to use. Just because some twit does something really silly (just guessing), does not make LiPos any more dangerous than a lot of the other stuff we deal with when flying.

Thoughts on what went wrong above:

Most LiPos used with ppg are multi-cell, but only in series. ie my own machine uses a 4 cell battery, with all 4 cells connected in series to give 4 x cell voltage. If any cell fails, then the battery is dead as no current can flow. This is called fail-safe. So the fault will not have been a cell failure. The usual reason is for failure is over-discharge. The user just keeps using the battery and takes the cell voltage below 2.5v (each cell starts at 4.2v). This is just user error and to me on a par with deliberately running your motor lean. Just don't do it - it will break! 

I always check my battery before flight and make sure it is 4.1v or higher per cell.  

[admin (Simon W)]

A tank of petrol next to a spark plug and a hot exhaust is arguably more dangerous. 

SW

 

[AndyB]

17 minutes ago, admin (Simon W) said:

A tank of petrol next to a spark plug and a hot exhaust is arguably more dangerous. 

SW

 

Here's a thought for you. Let's assume someone takes off without their fuel cap in place on the tank. The air/fuel ratio at the surface of the fuel is 100% fuel. Some distance away from the fuel tank there will be no fuel and 100% air. At some point between these there will be the perfect fuel/air ratio for an explosion. This is to me by far the most dangerous thing about our kit......leave the fuel cap off and the result could be a bang.

I have a video somewhere that shows this effect. We lit a large bonfire in the garden. We then took a 5 litre plastic container and put half litre of fuel in it. We left the lid off the container and through the container in a nice arc that would bring it down on top of the bonfire.

Guesses below pls as to what happened. 

 

[PatPux]

I've done similar. Any fuel that got out of the can settled in a nice blanket of vapour at ground level and when ignited as the can reached the bonfire, came right back to you with a big whooomf. And if the ground had been sloping towards you it would have surrounded you aswell.

[Casper]

But what would happen if I fly when it's -5 degree Celsius or colder? Will the battery drop to a dangerous voltage level? I understand that a protection circuit would prevent it to work, in this case there was no protection circuit at all.

I never check voltage on my GEL battery, it just works, and the engine charge it while I'm flying. Only issue is the extra weight, just like extra weight always will be an issue. Other than that I'm happy with GEL since they are very cheap to buy. I would change it to LIFEPO4 if I needed lower weight, now that LIFEPO4 have become much cheaper and also started to replace GEL in the stores. But I'm not sure if I would thrust the LiPo. I simply lack the knowledge to be sure that it's 100% fail safe. (just like lot's of RC pilots apparently do on youtube, with their expensive equipment)

Not sure if it's me or you who are silly here when comparing risk, while we actually have a case where it went wrong.
There is no reason to have a hot parts together with a fuel tank. And while everything we do put us into some sort of risk, that doesn't mean that something less dangerous can't make just the same mess. We almost always come to the conclusion that everything is pilot error, and when we have more things to handle we have more pilot mistakes. As I see it we can only reduce the risk and stay lucky that we don't miss anything, but by not even trying to stay safe we are definitely in for trouble.

I like to nerd down in all kinds of subjects and try to get expertise knowledge in most areas. But electricity and batteries technology is not one of those areas right now, so I still have to trust other peoples knowledge. When I see pictures and read about burning PPG pilots I definitely feel that this is a subject that requires that extra knowledge before I feel safe to use it.

My paramotor is designed so I quickly can drop the cage with motor and fuel tank, never by mistake, but always within a few seconds. I never heard about a case where it was needed before.

[alan_k]

As I understand it from the translation the battery failed due to overcharge.

I'm guessing it replaced a gel battery with no extra protection for overcharge, a definite requirement for Li-po's.

[AndyB]

1 hour ago, alan_k said:

As I understand it from the translation the battery failed due to overcharge.

I'm guessing it replaced a gel battery with no extra protection for overcharge, a definite requirement for Li-po's.

Sounds like it. Even with overcharge protection you are not safe. If one cell fails but stays closed circuit then the remaining cells get charged more. This is why only balance charging is ever recommended...and I can't see people attaching a balance charger onto their kit!